The invention relates to a detector for detecting the termination of sheet delivery for use in an apparatus having a sheet receptacle, such as a printing machine or magnetic record transfer apparatus, to detect the termination of sheet delivery as when sheets, such as printing papers or slave sheets, have been exhausted on the sheet receptacle.
Such detection of the absence of sheets may take place by using a photoelectric transducer element, for example, which is disposed in the path of the sheets so as to produce a sheet feed pulse normally in response to the delivery of a sheet, so that the occurrence of a variation in such pulse may be considered as representing the termination of sheet delivery. However, to achieve a high accuracy with a photoelectric transducer element, an electrical circuit and peripheral unit of high quality must be used, which is expensive. On the other hand, where such detection takes place at a location other than a sheet receptacle, it takes an appreciable period of time from the termination of sheet delivery to the detection. This results in an inconvenience, that the entire apparatus or part thereof may continue to idle, when it is desired to interrupt the operation of the entire apparatus with the signal detecting the termination of sheet delivery.
Another problem involved with a sheet processing apparatus is the fact that the immediate interruption of the operation of the entire apparatus when the supply of sheets on the sheet receptacle is exhausted leads to an inconvenience that the last sheet is left within the apparatus without being processed. To prevent such an inconvenience, the operation of the apparatus must be continued subsequent to the detection of the termination of sheet delivery until the last sheet is processed and displaced out of the apparatus.